1. Field of the Invention
The present invention relates generally to a calibration method of projection effect, and more particularly, the calibration method of projection effect is for detecting and calibrating the projection effect results from the fact that the object plane is not parallel with the image plane of the optical navigation system.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 illustrates optical devices of an optical mouse 1. As illustrated in FIG. 1, the optical devices of the optical mouse 1 comprise a light emitting module 10 and a sensor 12. The sensor 12 could be an image sensor. There is an image plane 120 on the sensor 12. The optical mouse 1 is performed on an object plane 20 of an object 2. There is a normal line of the object plane 20 on the object plane 20. The light emitted by the light emitting module 10 illuminates on the object plane 20 with an incident angle θi (the included angle between the incident light and the normal line of the object plane 20). The reflected light or the scattered light reflected from the object plane 20 are received by the sensor 12 in the direction of the reflected angle θr (the included angle between the reflected light and the normal line of the object plane 20), wherein the reflected angle θr could equal to the incident angle θi (that is to say, specular reflection) so as to enable the sensor 12 to receive the energy of the reflected light. Or the reflected angle θr could not be equal to the incident angle θi so as to enable the sensor 12 to receive the energy of the scattered light. If the image plane 120 is perpendicular to the direction of the reflected light but not parallel to the object plane 20 (that is to say, there is an included angle θs between the reflected light and the object plane 20), the sensor 12 will obtain better intensity of the optical signal due to such disposal so as to control the output of the light emitting module 10 to decrease the consumption of power and save electricity as expected.
After the sensor 12 receiving image, the image is delivered to the image processor. The image processor could be an integrated circuit (IC), an application-specific integrated circuit (ASIC), a digital signal processing (DSP), or a central processing unit (CPU). After receiving the image, the image processor proceeds with correlation comparison in real time, and calculates the information about the displacement (for example, the displacement Δx in x direction and the displacement Δy in y direction). By means of the information, the personal computer is able to control the mouse cursor to shift to the relative position.
However, when the said image plane 120 on the sensor 12 is not parallel to the object plane 20 of the object 2, and the object plane 20 moves relative to the optical device, the displacement on the object plane 20 will cause the projection effect on the image plane 120. Please refer to FIG. 2. FIG. 2 illustrates the projection effect between object plane 20 and the image plane 120. As illustrated in FIG. 2, the first direction A1 is on the object plane 20 and is perpendicular to the reflected light. The second direction A2 is on the object plane 20 and is perpendicular to the first direction A1. When there is a displacement d between the object plane 20 and the optical device in the first direction A1, the displacement of the reflected light on the image plane 120 in the relative first direction A1 will be d as well because the image plane 120 is parallel to the first direction A1. On the other hand, when there is a displacement d between the object plane 20 and the optical device in the second direction A2, the displacement of the reflected light on the image plane 120 in the relative second direction A2 will cause the projection effect because there is an included angle θs between the image plane 120 and the object plane 20, then the displacement of the reflected light on the image plane 120 in the relative second direction A2 will become d sin θs instead of d. In other words, the ratio of the displacement on the object plane 20 in the first direction A1 and that in the second direction A2 is 1:1, but on the other hand, the ratio of the displacement on the image plane 120 in the first direction A1 and that in the second direction A2 is 1:sin θs. The fact that the image plane 120 and the object plane 20 are not parallel results in the distortion of the optical mouse 1's locating trace. For example, when the optical mouse 1 moves in a circle trace on the object plane 20, the trace may become an ellipse on the image plane 120; when the optical mouse 1 moves in a square trace on the object plane 20, the trace may become a rectangle on the image plane 120.
Therefore, the main aspect of the invention is to provide a calibration method of projection effect for detecting and calibrating the projection effect results from the fact that the object plane is not parallel with the image plane of the optical navigation system. Moreover, the calibration method of projection effect can be applied to the calibrating of optical navigation systems such as optical mice, optical pens and optical positioning systems. The distortion of the projection effect can be solved by means of this method so as to improve the precision of the optical navigation system.